Dialium seed coprophagy in wild western gorillas: Multiple nutritional benefits and toxicity reduction hypotheses

Unraveling the relationship between the unusual feeding behaviors and the nutritional intake of endangered species may provide crucial information for understanding species response to habitat unpredictable changes. Primates occasionally re-ingest fruit seeds alongside ingestion of feces, a behavior called coprophagy. The nutritional benefit is one of the several non-mutual exclusive hypotheses proposed to explain this behavior. We investigated the ecological correlates of coprophagy in wild western gorillas. We tested whether coprophagy occurred during periods of lower fruit availability and whether it led to higher nutrient intake in comparison to the other food. Data integrated phenological, fecal and nutritional analyses of gorilla food with behavioral observations collected at two sites in Central Africa (Mbeli Bai: ad libitum observations on 15 groups/solitary males, October 2002-November 2005; Bai Hokou: 5-min scan on a habituated group, December 2004-December 2005). Coprophagy occurred at the end of the high-fruiting season in association of two Dialium species. Coprophagy correlated positively with the occurrence of Dialium spp. fruit in gorilla feces and in the feeding scans, and showed a positive trend with Dialium availability but not with total fruit availability. Nutritional comparison of Dialium seeds with other important gorilla food showed higher fat and mineral content, particularly of Mg, but also of phenols and tannins in Dialium seeds. We discuss how the effect of gut processing and gut heat via coprophagy may act as cooking-like effect: increasing the ability to maximize nutrient intake by concurrently softening fibers and decreasing the toxic effect of antifeedants, like in human traditional cooking. Our results support both the multiple nutritional benefit hypothesis and the toxicity reduction hypothesis. Since Dialium is precious timber, the importance of this tree for the critically endangered western gorillas should be taken with high consideration when planning controlled logging of degraded forests or in face of habitat changes.